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title="Permalink to [雪峰磁针石博客]python3快速入门教程3文本处理1正则表达式">[雪峰磁针石博客]python3快速入门教程3文本处理1正则表达式</a></h1>
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<abbr class="published" title="2018-09-02T10:45:00+08:00">
Published: 日 02 九月 2018
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By <a class="url fn" href="/author/andrew.html">andrew</a>
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<p>In <a href="/category/python.html">python</a>.</p>
</footer><!-- /.post-info --> <h2 id="_1">简介</h2>
<p>-- 后面有很多习题，可以先做题目再来看文章</p>
<p>参考资料：https://docs.python.org/3/howto/index.html</p>
<p>正则表达式(Regular expressions REs或regexes或regex patterns）本质是小的且高度专业化的编程语言。它嵌入到 Python 中，调用使用re模块。需要指定一些规则来描述那些你希望匹配的字符串集合。这些字符串集合可能包含英语句子、e-mail地址、TeX 命令，或任何你想要的东东。然后可以提出问题，例如“字符串是否匹配该模式？”或“模式是否匹配字符串？”。 您还可以使用RE修改字符串或以各种方式拆分它。</p>
<p>正则表达式模式被编译成字节码，然后由 C 语言写的匹配引擎执行。对于高级的使用，你可能需要关注匹配引擎是如何执行给定RE，并通过一定的方式来编写RE，以便产生运行得更快的字节码。</p>
<p>正则表达式语言小而严格，不是所有的字符处理都可以使用正则表达式。还有一些任务，可以使用正则表达式来完成，但是表达式非常复杂。在这种情况下编写 Python 代码来处理会更好些；尽管 Python 代码比精巧的正则表达式执行起来会慢一些，但可能会更容易理解。</p>
<h2 id="_2">简单的模式</h2>
<h3 id="_3">字符匹配</h3>
<p>大多数字母和字符会匹配它们自身。举个例子，正则表达式test将完全匹配字符串test(你可以启用不区分大小写模式，该正则表达式可以匹配Test或TEST)。</p>
<p>这条规则有例外; 有些字符是特殊的元字符，不匹配自身。 相反，它们匹配一些与众不同的东西，或者通过重复它们或改变它们的含义来影响RE的其他部分。</p>
<p>这是元字符的完整列表</p>
<div class="highlight"><pre><span></span><span class="o">.</span> <span class="o">^</span> <span class="err">$</span> <span class="o">*</span> <span class="o">+</span> <span class="err">?</span> <span class="p">{</span> <span class="p">}</span> <span class="p">[</span> <span class="p">]</span> \ <span class="o">|</span> <span class="p">(</span> <span class="p">)</span>
</pre></div>
<p>方括号 [ ]指定用于存放你需要匹配的字符集合。例如 [abc] 会匹配字符 a，b 或 c；[a-c] 可以实现相同功能。后者使用范围来表示与前者相同的字符集合。如果你想只匹配小写字母，你的 RE 可能写成 [a-z]。</p>
<p>注意方括号元字符在中不会触发特殊功能例如 [akm$] 会匹配字符 'a'，'k'，'m' 或 '$'。</p>
<p>你还可以匹配方括号中未列出的所有其它字符，开头添加 ^即可，例如 [^5] 会匹配除了 '5' 之外的任何字符。</p>
<p>元字符转义：前面加上一个反斜杠，以消除它们的特殊功能：[，\ 。</p>
<p>反斜杠后边跟一些字符还可以表示特殊的意义，例如表示十进制数字，表示所有的字母或者表示非空白的字符集合。</p>
<p>让我们来举个例子：\w 匹配任何单词字符。如果正则表达式以字节的形式表示，这相当字符类 [a-zA-Z0-9_]；如果正则表达式是一个字符串，\w 会匹配所有 Unicode 数据库（unicodedata 模块提供）中标记为字母的字符。你可以在编译正则表达式的时候，通过提供 re.ASCII 表示进一步限制 \w 的定义。</p>
<p>批注：re.ASCII 标志使得 \w 只能匹配 ASCII 字符，不要忘了，Python3 是 Unicode 的。</p>
<p>下边列举一些反斜杠加字符构成的特殊含义：</p>
<p>特殊字符 | 含义
| --- | --- |
\number |匹配相同编号的组。组从1开始编号。例如，(.+) \1匹配'the the'或'55 55'，但不匹配'thethe'（注意组后面的空格）。此特殊序列只能用于匹配前99个组。如果数字的第一个数字是0，或者数字是3个八进制数字长，则不会将其解释为组匹配，而是解释为具有八进制值编号的字符。在方括号内，所有数字转义都被视为字符。默认支持Unicode，中文标点也会作为边界。可以启用re.ASCII。
\d |匹配任何十进制数字，相当于类[0-9]
\D |与 \d 相反，匹配任何非十进制数字的字符，相当于 [^0-9]
\s | 匹配任何空白字符（包含空格、换行符、制表符等），相当于类 [\t\n\r\f\v]
\S |与 \s 相反，匹配任何非空白字符，当相于类 [^\t\n\r\f\v]
\w |匹配任何字符，设置了re.ASCII的情况下等同于[a-zA-Z0-9_]
\W |与 \w 相反，设置了re.ASCII的情况下等同于[^a-zA-Z0-9_]
\b |匹配单词的开始或结束
\B |与 \b 相反
\A |仅匹配字符串的开始。
\Z |仅匹配字符串末尾。</p>
<p>例如 [\s,.] 匹配任何空白字符（/s 的特殊含义），',' 或 ‘.’ 。</p>
<p>转义字符：</p>
<div class="highlight"><pre><span></span>\<span class="n">a</span> \<span class="n">b</span> \<span class="n">f</span> \<span class="n">n</span>
\<span class="n">r</span> \<span class="n">t</span> \<span class="n">u</span> \<span class="n">U</span>
\<span class="n">v</span> \<span class="n">x</span> \\
</pre></div>
<p>'.'匹配除了换行符以外的任何字符。如果设置re.DOTALL,它将匹配包括换行在内的任何字符。</p>
<h3 id="_4">重复</h3>
<p>'*' : 指定前一个字符匹配零次或者多次。</p>
<p>例如ca*t将匹配 ct(0 个 a)，cat（1 个字符 a），caaat（3 个字符 a），等等。需要注意的是，由于受到 C 语言的 int 类型大小的内部限制，正则表达式引擎会限制字符 'a' 的重复个数不超过 20 亿个；不过，通常我们工作也用不到那么大的数据，你未必有这么大的内存。</p>
<p>默认的是贪婪的，当你重复匹配一个 RE 时，匹配引擎会尝试尽可能多的去匹配。直到RE不匹配或者到了结尾，匹配引擎就会回退一个字符，然后再继续尝试。</p>
<p>表达式 a[bcd]*b，首先需要匹配字符 'a'，然后零个到多个 [bcd]，最后以 'b' 结尾。那现在想象一下，这个 RE 匹配字符串 abcbd 会怎样？</p>
<p>步骤 |匹配 |说明
| --- | --- | --- |
1| a| 匹配 RE 的第一个字符 'a'
2| abcbd| 引擎在符合规则的情况下尽可能地匹配 [bcd]<em>，直到该字符串的结尾
3| 失败 引擎尝试匹配 RE 最后一个字符 ‘b’，但当前位置已经是字符串的结尾，所以失败告终
4| abcb| 回退，所以 [bcd]</em> 匹配少一个字符
5| 失败| 再一次尝试匹配 RE 最后一个字符 'b'，但字符串最后一个字符是 'd'，所以失败告终
6| abc| 再次回退，所以 [bcd]* 这次只匹配 'bc'
7| abcb| 再一次尝试匹配这符 'b'，这一次字符串当前位置指向的字符正好是 'b'，匹配成功。最终，RE 匹配的结果是 abcb 。</p>
<p>另一个实现重复的元字符是 +，用于指定前一个字符匹配一次或者多次。</p>
<p>要特别注意 * 和 + 的区别：* 匹配的是零次或者多次，所以被重复的内容可能压根儿不会出现；+ 至少需要出现一次。例如 ca+t 会匹配 cat 和 caaat，但不会匹配 ct 。</p>
<p>还有两个表示重复的元字符，一个是问号?: 字符匹配零次或者一次。</p>
<p>元字符 {m,n}（m 和 n 都是十进制数），必须匹配 m 次到 n 次之间。例如 a/{1,3}b 会匹配 a/b，a//b 和 a///b 。但不会匹配 ab(没有斜杠)；也不会匹配 a////b(斜杠超过三个)。</p>
<p>你可以省略 m 或者 n，这样的话，引擎会用合理的值代替。 m默认为0；n 默认为 20 亿。</p>
<p>{0,}跟’*‘ 是一样的；{1,}跟‘+’是一样的；{0,1} 跟？是一样的。不过还是鼓励大家记住并使用 * 、+ 和 ?，因为这些字符更短并且更容易阅读。</p>
<h3 id="_5">习题</h3>
<p>1, 下面那些不是python3正则表达式的元字符：</p>
<p>A $ B - C * D ？ E /</p>
<p>参考答案：B E</p>
<p>2,python3正则表达式r'\bfoo\b'匹配下面哪些字符串</p>
<p>A 'foo' B 'foo.' C '(foo)' D 'bar foo baz' E 'foobar' F 'foo3'</p>
<p>参考答案：A B C D</p>
<p>3,python3正则表达式r'\bfoo\b'匹配下面哪些字符串</p>
<p>A 'foo，' B 'foo。' C '(foo！' D 'bar foo baz' E 'foobar' F 'foo3'</p>
<p>参考答案：A B C D</p>
<p>4，下面python3正则表达式元字符的描述哪些是错误的。
A. 默认\w不能匹配汉字
B. 默认\w能匹配汉字
C. 默认.能匹配换行符
D. 默认.不能匹配换行符</p>
<p>参考答案：A C </p>
<h2 id="_6">使用正则表达式</h2>
<p>Python通过re模块提供正则表达式支持，并可将正则表达式编译成对象，用它们来进行匹配。</p>
<h3 id="_7">编译正则表达式</h3>
<p>正则表达式编译为模式对象，该对象拥有各种方法，如查找模式匹配或者执行字符串替换。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="kn">import</span> <span class="nn">re</span>
<span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'ab*'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">p</span>
<span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'ab*'</span><span class="p">)</span>
</pre></div>
<p>re.compile()也接受可选的flags 参数，用于开启各种特殊功能和语法变化。</p>
<p>简单的例子：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'ab*'</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">IGNORECASE</span><span class="p">)</span>
</pre></div>
<p>正则表达式作为字符串参数传给 re.compile() 。由于正则表达式并不是 Python语言的核心部分，因此没有为它提供特殊的语法支持，所以正则表达式只能以字符串的形式表示。</p>
<h3 id="_8">原始字符串</h3>
<p>'\section' 要用'\\section'表示。不巧，Python 字符串也使用 '\' 表示字符 '\'。原始字符串则方便得多：r"\section"即可。</p>
<h3 id="_9">匹配</h3>
<p>模式对象的常用方法：</p>
<p>方法 |功能
| --- | --- |
match() |判断正则表达式是否从开始处匹配一个字符串
search() |遍历字符串，找到正则表达式匹配的第一个位置
findall() |遍历字符串，找到正则表达式匹配的所有位置，并以列表的形式返回
finditer() |遍历字符串，找到正则表达式匹配的所有位置，并以迭代器的形式返回</p>
<p>如果没有找到任何匹配的话，match() 和 search() 会返回 None；如果匹配成功，则会返回匹配对象（match object），包含所有匹配的信息：例如从哪儿开始，到哪儿结束，匹配的子字符串等等。</p>
<p>python自带了正则表达式调试工具redemo.py：</p>
<p><img alt="图片.png" src="https://upload-images.jianshu.io/upload_images/10819934-725670e086543b42.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240"></p>
<p>实例：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="kn">import</span> <span class="nn">re</span>
<span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'[a-z]+'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">p</span>
<span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'[a-z]+'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">""</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">""</span><span class="p">))</span>
<span class="bp">None</span>
<span class="o">>>></span> <span class="n">m</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s1">'tempo'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">m</span>
<span class="o"><</span><span class="n">re</span><span class="o">.</span><span class="n">Match</span> <span class="nb">object</span><span class="p">;</span> <span class="n">span</span><span class="o">=</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">5</span><span class="p">),</span> <span class="n">match</span><span class="o">=</span><span class="s1">'tempo'</span><span class="o">></span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">()</span>
<span class="s1">'tempo'</span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">(),</span> <span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">()</span>
<span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">5</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">span</span><span class="p">()</span>
<span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">5</span><span class="p">)</span>
</pre></div>
<p>匹配对象包含了很多方法和属性，以下几个是最重要的：</p>
<p>方法 |功能
| --- | --- |
group() |返回匹配的字符串
start() |返回匹配的开始位置
end() |返回匹配的结束位置
span() |返回元组表示匹配位置(start, end) </p>
<p>match的start总是0，search() 方法则不一定了：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s1">'::: message'</span><span class="p">))</span>
<span class="bp">None</span>
<span class="o">>>></span> <span class="n">m</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'::: message'</span><span class="p">);</span> <span class="k">print</span><span class="p">(</span><span class="n">m</span><span class="p">)</span>
<span class="o"><</span><span class="n">re</span><span class="o">.</span><span class="n">Match</span> <span class="nb">object</span><span class="p">;</span> <span class="n">span</span><span class="o">=</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="mi">11</span><span class="p">),</span> <span class="n">match</span><span class="o">=</span><span class="s1">'message'</span><span class="o">></span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">()</span>
<span class="s1">'message'</span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">span</span><span class="p">()</span>
<span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="mi">11</span><span class="p">)</span>
</pre></div>
<p>在实际应用中，最常用的方法是将匹配对象存放在局部变量中，并检查其返回值是否为 None 。</p>
<div class="highlight"><pre><span></span><span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span> <span class="o">...</span> <span class="p">)</span>
<span class="n">m</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">match</span><span class="p">(</span> <span class="s1">'string goes here'</span> <span class="p">)</span>
<span class="k">if</span> <span class="n">m</span><span class="p">:</span>
<span class="k">print</span><span class="p">(</span><span class="s1">'Match found: '</span><span class="p">,</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">())</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">print</span><span class="p">(</span><span class="s1">'No match'</span><span class="p">)</span>
</pre></div>
<p>有两个方法可以返回所有的匹配结果，一个是 findall()，一个是 finditer() 。</p>
<p>findall() 返回的是一个列表：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\d+'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">findall</span><span class="p">(</span><span class="s1">'12 drummers drumming, 11 pipers piping, 10 lords a-leaping'</span><span class="p">)</span>
<span class="p">[</span><span class="s1">'12'</span><span class="p">,</span> <span class="s1">'11'</span><span class="p">,</span> <span class="s1">'10'</span><span class="p">]</span>
</pre></div>
<p>而 finditer() 则是将匹配对象作为迭代器返回：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">iterator</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">finditer</span><span class="p">(</span><span class="s1">'12 drummers drumming, 11 ... 10 ...'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">iterator</span>
<span class="o"><</span><span class="n">callable_iterator</span> <span class="nb">object</span> <span class="n">at</span> <span class="mi">0</span><span class="n">x</span><span class="o">...></span>
<span class="o">>>></span> <span class="k">for</span> <span class="n">match</span> <span class="ow">in</span> <span class="n">iterator</span><span class="p">:</span>
<span class="o">...</span> <span class="k">print</span><span class="p">(</span><span class="n">match</span><span class="o">.</span><span class="n">span</span><span class="p">())</span>
<span class="o">...</span>
<span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
<span class="p">(</span><span class="mi">22</span><span class="p">,</span> <span class="mi">24</span><span class="p">)</span>
<span class="p">(</span><span class="mi">29</span><span class="p">,</span> <span class="mi">31</span><span class="p">)</span>
</pre></div>
<h3 id="_10">模块级函数</h3>
<p>re 模块同时还提供了一些全局函数，例如 match()，search()，findall()，sub() 等。这些函数跟模式对象同名方法一样，只是增加了为正则表达式字符串的第一个参数。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s1">'From\s+'</span><span class="p">,</span> <span class="s1">'Fromage amk'</span><span class="p">))</span>
<span class="bp">None</span>
<span class="o">>>></span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s1">'From\s+'</span><span class="p">,</span> <span class="s1">'From amk Thu May 14 19:12:10 1998'</span><span class="p">)</span>
<span class="o"><</span><span class="n">re</span><span class="o">.</span><span class="n">Match</span> <span class="nb">object</span><span class="p">;</span> <span class="n">span</span><span class="o">=</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">5</span><span class="p">),</span> <span class="n">match</span><span class="o">=</span><span class="s1">'From '</span><span class="o">></span>
</pre></div>
<p>这些函数帮你自动创建模式对象，并调用相关的函数。它们还将编译好的模式对象存放在缓存中，以便将来可以快速地直接调用。</p>
<p>在循环中大量的使用正则表达式，预编译的话可以节省一些函数调用，用模式的方法更好。但如果是循环外部，因为有内部缓存机制，两者效率相差无几。</p>
<h3 id="_11">编译标识</h3>
<p>编译标识可修改正则表达式的工作方式。在 re 模块下，编译标识均有完整名和简写，例如 IGNORECASE 简写是 I。</p>
<p>标志 |含义
| --- | --- |
ASCII，A |使得转义符号 \w，\b，\s 和 \d 只能匹配 ASCII 字符
DOTALL，S |使得 . 匹配任何符号，包括换行符
IGNORECASE，I |不区分大小写
LOCALE，L |支持当前语言（区域）设置
MULTILNE，M |多行匹配，影响 ^ 和 $
VERBOSE，X（for'extended'） |启用详细的正则表达式, 更简洁且更容易理解。 </p>
<p>下面我们来详细讲解一下它们的含义：</p>
<ul>
<li>I</li>
</ul>
<p>IGNORECASE</p>
<p>不区分大小写。举个例子，正则表达式[a-z] 或[A-Z]会匹配对应的小写字母会匹配52个ASCII字母。还有4个非ASCII字母：'İ'(U + 0130，拉丁大写字母I上面带点)，'ı'(U + 0131，拉丁文小写字母无点i)，'s'(U + 017F，拉丁文小 字母长s)和'K'(U + 212A，开尔文标志)。 Spam 将匹配'Spam'，'spam'，'spAM'或'ſpam'（后者仅在Unicode模式下匹配）。 此小写不考虑当前区域设置; 如果您还设置了LOCALE标志，它也会。</p>
<ul>
<li>L</li>
</ul>
<p>LOCALE</p>
<p>使得 \w，\W，\b 和 \B和大小写依赖当前的语言(区域)环境，而不是 Unicode 数据库。</p>
<p>区域设置是 C 语言的功能，主要作用是消除不同语言之间的差异。例如你正在处理的是法文文本，你想使用 \w+ 来匹配单词，但是 \w 只是匹配 [A-Za-z] 中的单词，并不会匹配那些法文特殊符号。python3已经推荐使用Unicode，不建议使用LOCALE。</p>
<ul>
<li>M</li>
</ul>
<p>MULTILNE</p>
<p>通常 ^ 只匹配字符串的开头，而 \$ 匹配字符串的结尾。该标识设置时，^ 不仅匹配字符串的开头，还匹配行首；$ 不仅匹配字符的结尾，还匹配行尾。</p>
<ul>
<li>S</li>
</ul>
<p>DOTALL</p>
<p>. 可以匹配任何字符，包括换行符。如果不使用这个标志，. 将匹配除换行的所有字符。</p>
<ul>
<li>A</li>
</ul>
<p>ASCII
使得 \w，\W，\b，\B，\s 和 \S 只匹配 ASCII 字符，而不是全Unicode匹配。这个标识仅对Unicode模式有意义，并忽略字节模式。</p>
<ul>
<li>X</li>
</ul>
<p>VERBOSE</p>
<p>这个标识使你的正则表达式可以写得更可读灵活，空格会被忽略(除了出现在字符类中和使用反斜杠转义的空格)；同时允许你在正则表达式字符串使用注释，# 符号后边的内容是注释(除了出现在字符类中和使用反斜杠转义的 #)。</p>
<p>下边是使用 re.VERBOSE 的例子，：</p>
<div class="highlight"><pre><span></span><span class="n">charref</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">"""</span>
<span class="s2"> &[#] # Start of a numeric entity reference</span>
<span class="s2"> (</span>
<span class="s2"> 0[0-7]+ # Octal form</span>
<span class="s2"> | [0-9]+ # Decimal form</span>
<span class="s2"> | x[0-9a-fA-F]+ # Hexadecimal form</span>
<span class="s2"> )</span>
<span class="s2"> ; # Trailing semicolon</span>
<span class="s2">"""</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">VERBOSE</span><span class="p">)</span>
<span class="c1"># 没有注释</span>
<span class="n">charref</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">"&#(0[0-7]+"</span>
<span class="s2">"|[0-9]+"</span>
<span class="s2">"|x[0-9a-fA-F]+);"</span><span class="p">)</span>
</pre></div>
<h3 id="_12">习题</h3>
<p>1，下面关于python3 正则模式的说哪些是错误的？</p>
<p>A. match() 可以返回多个匹配
B. search() 必须从开头开始匹配
C. findall() 以迭代器的形式返回
D. finditer() 以列表的形式返回</p>
<p>答案：ABCD</p>
<p>2，python3 正则表达式re.compile('spam', re.IGNORECASE)匹配哪些字符串？
A.'Spam' B. 'spam' C. 'spAM' D. 'ſpam' E.'pam'</p>
<p>答案：ABCD</p>
<h2 id="_13">更多关于模式</h2>
<h3 id="_14">更多元字符</h3>
<ul>
<li>I</li>
</ul>
<p>或操作符，对两个正则表达式进行操作。如果 A 和 B 是正则表达式，A | B 会匹配 A 或 B 中出现的任何字符。为了能够更加合理的工作，| 的优先级非常低。例如 Crow|Servo匹配'Crow'或'Servo',，而不是匹配'Cro'、 'w' 、'S'、'ervo'.。</p>
<p>同样，我们使用 | 来匹配 '|' 字符本身；或者包含在一个字符类中，像这样 [|] 。</p>
<ul>
<li>^</li>
</ul>
<p>匹配字符串开始。在 MULTILNE 中，每当遇到换行符就会立刻进行匹配。如果你只希望匹配位于字符串开头的单词 From，那么你的正则表达式可以写为 ^From</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'^From'</span><span class="p">,</span> <span class="s1">'From Here to Eternity'</span><span class="p">))</span>
<span class="o"><</span><span class="n">re</span><span class="o">.</span><span class="n">Match</span> <span class="nb">object</span><span class="p">;</span> <span class="n">span</span><span class="o">=</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span> <span class="n">match</span><span class="o">=</span><span class="s1">'From'</span><span class="o">></span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'^From'</span><span class="p">,</span> <span class="s1">'Reciting From Memory'</span><span class="p">))</span>
<span class="bp">None</span>
</pre></div>
<ul>
<li>$</li>
</ul>
<p>匹配字符串的结束和行尾。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'}$'</span><span class="p">,</span> <span class="s1">'{block}'</span><span class="p">))</span>
<span class="o"><</span><span class="n">re</span><span class="o">.</span><span class="n">Match</span> <span class="nb">object</span><span class="p">;</span> <span class="n">span</span><span class="o">=</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span> <span class="mi">7</span><span class="p">),</span> <span class="n">match</span><span class="o">=</span><span class="s1">'}'</span><span class="o">></span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'}$'</span><span class="p">,</span> <span class="s1">'{block} '</span><span class="p">))</span>
<span class="bp">None</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'}$'</span><span class="p">,</span> <span class="s1">'{block}</span><span class="se">\n</span><span class="s1">'</span><span class="p">))</span>
<span class="o"><</span><span class="n">re</span><span class="o">.</span><span class="n">Match</span> <span class="nb">object</span><span class="p">;</span> <span class="n">span</span><span class="o">=</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span> <span class="mi">7</span><span class="p">),</span> <span class="n">match</span><span class="o">=</span><span class="s1">'}'</span><span class="o">></span>
</pre></div>
<ul>
<li>A</li>
</ul>
<p>匹配字符串开始，如果没有设置 MULTILINE 标志的时候，\A 和 ^ 的功能是一样的；但如果设置了 MULTILNE 标志， ^ 会对字符串的每一行都进行匹配。</p>
<ul>
<li>Z</li>
</ul>
<p>匹配字符串的结束。</p>
<ul>
<li>b</li>
</ul>
<p>单词边界，这是只匹配单词的开始和结尾的零宽断言。单词定义为字母数字的序列，所以单词的结束指的是空格或者非字母数字的字符。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\bclass\b'</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'no class at all'</span><span class="p">))</span>
<span class="o"><</span><span class="n">re</span><span class="o">.</span><span class="n">Match</span> <span class="nb">object</span><span class="p">;</span> <span class="n">span</span><span class="o">=</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">8</span><span class="p">),</span> <span class="n">match</span><span class="o">=</span><span class="s1">'class'</span><span class="o">></span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'the declassified algorithm'</span><span class="p">))</span>
<span class="bp">None</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'one subclass is'</span><span class="p">))</span>
<span class="bp">None</span>
</pre></div>
<p>在使用这些特殊的序列的时候，有两点是需要注意的：第一是Python 的字符串跟正则表达式在有些字符上是有冲突的。比如说在 Python 中，\b 表示的是退格符，ASCII 码值是 8。</p>
<p>下边例子中，我们故意不写表示原始字符串的 'r'，结果确实大相庭径：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'</span><span class="se">\b</span><span class="s1">class</span><span class="se">\b</span><span class="s1">'</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'no class at all'</span><span class="p">))</span>
<span class="bp">None</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'</span><span class="se">\b</span><span class="s1">'</span> <span class="o">+</span> <span class="s1">'class'</span> <span class="o">+</span> <span class="s1">'</span><span class="se">\b</span><span class="s1">'</span><span class="p">))</span>
<span class="o"><</span><span class="n">re</span><span class="o">.</span><span class="n">Match</span> <span class="nb">object</span><span class="p">;</span> <span class="n">span</span><span class="o">=</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">7</span><span class="p">),</span> <span class="n">match</span><span class="o">=</span><span class="s1">'</span><span class="se">\x08</span><span class="s1">class</span><span class="se">\x08</span><span class="s1">'</span><span class="o">></span>
</pre></div>
<p>第二点是在字符类中不能使用这个断言。在字符类中，\b 只是用来表示退格符。</p>
<ul>
<li>\B</li>
</ul>
<p>与 \b 的含义相反，\B 表示非单词边界的位置。</p>
<h3 id="_15">分组</h3>
<p>仅仅知道正则表达式是否匹配是不够的，正则表达式通常使用分组的方式分别对不同内容进行匹配。</p>
<p>下例子将 RFC-822 头用 “:” 号分成名字和值：</p>
<div class="highlight"><pre><span></span><span class="n">From</span><span class="p">:</span> <span class="n">author</span><span class="nd">@example.com</span>
<span class="n">User</span><span class="o">-</span><span class="n">Agent</span><span class="p">:</span> <span class="n">Thunderbird</span> <span class="mf">1.5</span><span class="o">.</span><span class="mf">0.9</span> <span class="p">(</span><span class="n">X11</span><span class="o">/</span><span class="mi">20061227</span><span class="p">)</span>
<span class="n">MIME</span><span class="o">-</span><span class="n">Version</span><span class="p">:</span> <span class="mf">1.0</span>
<span class="n">To</span><span class="p">:</span> <span class="n">editor</span><span class="nd">@example.com</span>
</pre></div>
<p>先用正则表达式匹配整个RFC-822头，使用一个组来匹配头的名字，另一个组匹配名字对应的值。</p>
<p>正则表达式使用元字符'(', ')' 来划分组。'(', ')' 元字符跟数学表达式中的小括号含义差不多；它们将包含在内部的表达式组合在一起，所以你可以对组的内容使用重复操作的元字符，例如 *，+，? 或者 {m,n} 。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'(ab)*'</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s1">'ababababab'</span><span class="p">)</span><span class="o">.</span><span class="n">span</span><span class="p">())</span>
<span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">10</span><span class="p">)</span>
</pre></div>
<p>用'（'，'）'表示的组也捕获它们匹配的文本的起始和结束索引; 这可以通过将参数传递给ggroup()，start()，end() 和 span() 来检索。 组从0开始编号。组0始终存在; 它是整个RE，因此匹配对象方法都将组0作为其默认参数。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'(a)b'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">m</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s1">'ab'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">()</span>
<span class="s1">'ab'</span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="s1">'ab'</span>
</pre></div>
<p>子组从左到右进行编号，子组也允许嵌套，我们可以通过从左往右来统计左括号 ( 来确定子组的序号。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s1">'(a(b)c)d'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">m</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s1">'abcd'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="s1">'abcd'</span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="s1">'abc'</span>
<span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="s1">'b'</span>
</pre></div>
<p>group() 方法可传入多个子组的序号：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">)</span>
<span class="p">(</span><span class="s1">'b'</span><span class="p">,</span> <span class="s1">'abc'</span><span class="p">,</span> <span class="s1">'b'</span><span class="p">)</span>
</pre></div>
<p>groups() 方法一次性返回所有的子组匹配的字符串：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">()</span>
<span class="p">(</span><span class="s1">'abc'</span><span class="p">,</span> <span class="s1">'b'</span><span class="p">)</span>
</pre></div>
<p>反引用可以在后面的位置使用先前匹配过的内容，用法是反斜杠加上数字。例如 \1 表示引用前边成功匹配的序号为 1 的子组。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">p</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\b(\w+)\s+\1\b'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">p</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'Paris in the the spring'</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">()</span>
<span class="s1">'the the'</span>
</pre></div>
<h3 id="_16">习题</h3>
<p>1, python3正则表达式compile('Crow|Servo')匹配哪些内容：</p>
<p>A 'Crow' B 'foo。' C Servw' D 'Cro' E 'Serv' F 'Servo'</p>
<h3 id="_17">重复</h3>
<p>参考答案：A F</p>
<p>2, python3正则表达式要匹配'|'，可以采用如下哪些方法：</p>
<p>A '||' B '|' C '[|]' D '$|' </p>
<p>参考答案：B C </p>
<p>3,关于python3正则表达式，下面哪些说法是正确的</p>
<p>A re.findall(r'^From', 'From Here to Eternity\nFrom', re.MULTILINE) 返回长度为2的列表
B re.findall(r'^From', 'From Here to Eternity\nFrom') 返回长度为2的列表
C re.findall(r'^From', ' From Here to Eternity\nFrom', re.MULTILINE) 返回长度为2的列表
D re.findall(r'\bFrom', ' From Here to Eternity\nFrom', re.MULTILINE) 返回长度为2的列表</p>
<p>参考答案：A D</p>
<p>4,关于python3正则表达式，下面哪些说法是正确的</p>
<p>A re.search(r'\bclass\b', 'no class at all')能成功匹配
B re.search('\bclass\b', 'no class at all')能成功匹配
C re.search(r'\bclass\b', 'no class at all')不能能成功匹配
D re.search('\bclass\b', 'no class at all')不能成功匹配</p>
<p>参考答案：A D</p>
<p>待整理： notepad++ 正则 http://docs.notepad-plus-plus.org/index.php/Regular_Expressions</p>
<h2 id="_18">参考资料</h2>
<ul>
<li>python测试等IT技术支持qq群： 144081101(后期会录制视频存在该群群文件) 591302926 567351477 钉钉免费群：21745728</li>
<li>道家技术-手相手诊看相中医等钉钉群21734177 qq群：391441566 184175668 338228106 看手相、面相、舌相、抽签、体质识别。服务费50元每人次起。请联系钉钉或者微信pythontesting</li>
<li><a href="https://china-testing.github.io/python3_crash8.html">本文最新版本地址</a></li>
<li><a href="https://github.com/china-testing/python-api-tesing">本文涉及的python测试开发库</a> 谢谢点赞！</li>
<li><a href="https://github.com/china-testing/python-api-tesing/blob/master/books.md">本文相关海量书籍下载</a></li>
<li><a href="https://china-testing.github.io/testing_training.html">接口自动化性能测试线上培训大纲</a></li>
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